1. Field of the Invention
The present invention relates to a system, method, transmitter, and receiver capable of efficiently converting a frame rate into a higher rate using a motion vector, in the case where an apparatus that decodes a video signal encoded using the motion vector is provided separately from an apparatus that converts the decoded video signal into a signal of a frame rate higher than that of the decoded video signal and that displays the decoded video signal at a higher frame rate.
2. Description of the Related Art
A decoding unit that decodes a compressed video signal encoded by an encoding method such as MPEG-2 using a motion vector to retrieve a video signal is mounted on a DVD player, digital broadcast tuner, set-top box, and the like. The compressed video signal includes a frame encoded by intra-frame coding that compresses each actual frame and a frame encoded by inter-frame coding that compresses a difference from another reference frame. When the difference is obtained using motion predictive compensation in the inter-frame coding, an image is generated using the motion vector to predict a moving destination of a video block contained in another reference frame, and the difference from the predicted image is obtained to efficiently perform encoding.
On the other hand, in order to reduce a blur in a moving image and to smoothly represent moving images, a frame rate converting unit that performs a frame rate conversion by generating an interpolated frame between frames of video has been mounted on a television receiver and the like. Although a plurality of methods are available as the method of generating the interpolated frame, a comparatively accurate interpolated frame can be generated by a method using a motion vector between the video blocks in the frames previous and subsequent to the interpolated frame to predict the interpolated frame picture that is an intermediate image of those frames.
However, a calculation cost to detect the motion vector is not small, because whether the same image exists in the respective video blocks contained in two frames is checked using various combinations of positions. Further, in the case where the video the frame rate of which was converted is displayed in real time, higher computational capability may be required, since the motion vector needs to be detected within a limited period of time until the next frame after the conversion is displayed. Japanese Unexamined Patent Application Publication No. 2003-333540 (paragraphs No. 0010 through 0011, and FIG. 1) discloses a frame rate converter that uses the motion vector obtained in the above-described decoding processing also for the frame rate conversion, thereby greatly reducing the calculation cost and efficiently performing the frame rate conversion.
The frame rate converter disclosed in Japanese Unexamined Patent Application Publication No. 2003-333540 includes a decoding unit 100 and a frame rate converting unit 101 which are provided in the same display apparatus (such as a television receiver), as shown in FIG. 1. A video signal and a motion vector are sent from the decoding unit 100 to the frame rate converting unit 101 through an internal bus or the like.
A video buffer 102 stores the video signal in the frame rate converting unit 101 and an interpolated vector generating unit 103 generates an interpolated vector using the motion vector having been used for predicting pictures previous and subsequent to the interpolated frame. Subsequently, an interpolated frame generating unit 104 reads the pictures previous and subsequent to the interpolated frame from the video buffer 102 and generates a predicted frame at a position in terms of time of the interpolated frame using the interpolated vector. Further, a selector 105 selects and outputs the picture (real frame) stored in the video buffer 102 and the generated interpolated frame according to the frame rate.